Calculate the rent of a decreasing annuity at 8% interest compounded quarterly with payments made every quarter-year for 7 years and present value $78,000.

You can use trigonometry to graph the changes in high and low tides for a particular location. Along the coast, the tides are of particular interest. They are affected by the gravitational pull of both the moon and the sun. The high tides and low tides follow a periodic pattern that you can model with the sine function.

(Not my answer).